The conquest of fire by primitive man was one of the most important milestones of pre-history and can truly be said to be the first step toward civilization. The great benefits of this early achievement have been obtained at the cost of the occasional destruction of life and property by accidental fires.
In certain aspects of modern civilization, there is extreme vulnerability to accidental fires because of an inability of those nearby to flee the scene. For example, a fire in an airplane, or in a submarine, can kill all passengers and crew unless it is first contained and then extinguished.
Recently, fire-block materials have been developed which are effective, even in thin layers, for blocking flame spread to a greater extent than the materials previously known.
One such material is described and claimed in co-assigned U.S. patent application Ser. No. 103,064, filed by Anderson et al. on Nov. 25, 1987, of which application the present application is a continuation-in-part. This material is a laminate of a silicone foam and a support layer. It has a flame spread index of zero at 20 minutes of exposure in accordance with ASTM E-162 and is capable, in a thickness of 1/16 inch, of blocking a flame of 1900.degree. F. for more than one hour.
The support layer of the aforesaid laminate is preferably a fiberglass woven cloth. The silicone foam contains alumina trihydrate as a filler and is the cured elastomeric reaction product of a vinyl-terminated polysiloxane containing --Si(CH.sub.3).sub.2 O-- units and an organohydrogen siloxane containing --Si(H)(CH.sub.3)O-units.
When it is desired to utilize the aforementioned laminate, or other silicone-based fire-block material, to cover an inflammable, or other heat-destructible object or layer, it is necessary to glue the laminate to the surface of the heat destructible layer, particularly to a vertical surface thereof or to the underside of a horizontal surface. Underside horizontal surfaces are particularly vulnerable to flames because hot air rising from a flame imparts directly on such underside horizontal surfaces and generally remains in contact long enough to inflame or damage susceptible materials.
For optimum flame retardency, it is necessary that the glue, or adhesive, holding the fire-block layer to its substrate be, itself, a fire-block material. Otherwise, the fire will spread through the turning of the adhesive.
A room or compartment, for example, may be lined on all of its interior walls with the fire-block laminate of said application Ser. No. 103,064. Nevertheless, fire will spread from such a room or compartment by ignition of the adhesive, particularly at exposed surfaces, if the adhesive is not, itself, non-burning.
Prior to this invention, adhesive materials have been sold which have been represented to be fire-retardant. These materials are capable of delaying the spread of a fire, but they are ignitable when flame contact is maintained and therefore do not provide prolonged fire-block protection. In addition, the fire retardant adhesive materials heretofore available have generally been of high viscosity because of high loading of solid fire retardant fillers. Such highly viscous materials are difficult to spread and are not suitable for spray application.